Many products such as wine and other products are typically stored in glass bottles and sealed with a stopper made of natural or synthetic cork. Natural cork is acquired from the Cork Oak (Quercus suber) predominately in Portugal and other countries surrounding the Mediterranean Sea. It is utilized in a variety of products including cork stoppers for wine and other beverages. As an enclosure for liquids, cork has the desirable properties of being impermeable to liquids and gases, as well as compressible. The quality of cork enclosures is determined by the presence and size of defects, voids, or cracks. Methods of non-destructive evaluation (NDE) of corks include visible inspection of visible cracks and defects either by human experts or camera systems, chemical analysis (including cork soaks) for the presence of 2,4,6-trichloroanisole (TCA), and x-ray tomography.
Prior to bottling, the cork may be treated with chlorinated chemicals to kill bacteria. However, not all of the bacteria are killed. The surviving bacteria can spoil the wine through various mechanisms. The most prevalent and widely understood is the conversion of residual chlorinated compounds in treated cork by bacteria to TCA. After bottling, the TCA leaches into the wine giving it a musty, mushroom flavored taint. This type of spoilage is called cork taint, “corking” or “corked wine”. The severity can range from a lack of aftertaste (or “finish”) to a taste and aroma of mold or wet cardboard. Other mechanisms for wine spoilage include the presence of 2-methoxy-3,5-dimethylpyranzine (herein referred to as “MDMP”), phenol, and contamination of “clean” corks by other sources of mold or bacteria that are present in the bottling process. M. A. Sefton and R. F. Simpson, “Compounds causing cork taint and the factors affecting their transfer from natural cork closures to wine—a review”, Australian Journal of Grape and Wine Research 11, 226-240 (2005).
“Corking” affects all types and qualities of wines, typically spoiling 3%-5% of all wines that use natural cork as a stopper. The problem of “corked” wine is even more insidious as there is no visual indication that a particular cork prior to bottling will result in cork taint or that a previously bottled wine has been “corked”. Therefore consumers, collectors, auction houses, wine producers, and/or wine bottlers have no way of determining whether the wine is “corked” until they have already purchased and opened the bottle. This problem could be alleviated, however, if the wine bottle could be tested before it is purchased to see if it contains the bacteria responsible for “corking” the wine. A related issue intrinsic to wine producers and wine bottlers is determining whether the cork is tainted prior to being used as a sealing apparatus or whether the cork has a high likelihood of developing taint after bottling. Accordingly wine producers and wine bottlers would greatly benefit from a non-destructive method and apparatus to determine the presence of taint or the likelihood of the cork developing taint prior to using the cork as a sealing apparatus.
Most corks are punched with the long axis of the cork perpendicular to the lenticels. The lenticels allow for the interchange of gases between the atmosphere and in the interior structure of the cork tree. It has been shown that TCA does not quickly permeate down the length of the cork, but propagates much more quickly perpendicular to the long axis. Consequently, only when contaminated parts of the cork are in direct contact with the wine (approximately the first few millimeters of cork) does transfer of TCA into the wine take place. While there are several screening methods used by wine companies to screen cork closures, most notably, soaking the corks in wine and subsequent testing based on sensory assessments or analytic chemical analysis, there is currently no cork screening method that has been demonstrated to accurately predict the level of taint in a bottle of wine. In addition, presently available methods are slow and only test a representative selection of the corks to be used in bottling because these methods are destructive. Accordingly, since all the corks are not tested individually, there may be a percentage of tainted cork that is not detected that is ultimately used in the bottling process.
Electromagnetic radiation in the THz frequency lies between the far infrared (which is generated by optical means) and microwave (which is generated by electrical means) regions of the electromagnetic spectrum. Because THz waves lie at the edge of the capabilities of both electrical and optical wave generation techniques, it was previously difficult, if not impossible, to generate THz waves needed for THz spectroscopy. Advances in the art have been able to produce radiation in the THz spectrum that could be used for THz spectroscopy. THz radiation is readily transmitted through most non-metallic and non-aqueous mediums, thus enabling THz systems to “see through” concealing barriers such as plastic packaging, corrugated cardboard, clothing, shoes, book bags, glass, etc. in order to probe the materials contained within. This has given rise to a whole host of applications for spectroscopy in this region, including the detection of biological weapons and explosives, non-destructive testing of pharmaceutical coatings, biomedical imaging, atmospheric gas detection, chemicals in crystalline form and materials identification.